Cancer can be treated by exposing the cancerous cells to radiation (alpha, beta or gamma). Gamma radiation travels through most materials, beta radiation through fewer, and alpha radiation through very little. In the context of TAT, it means that if alpha radiation can be delivered directly to the cancer cells, it will kill the cancerous cells without also damaging close-by healthy tissue. It sounds simple enough, but the challenge lies in getting an alpha-emitting substance very close to (or inside) the cancerous cells without it also going to other parts of the body.
The field of targeted alpha therapy research aims to solve this problem.
There are only a few alpha-emitting radioactive isotopes that have suitable half-lives and decay properties to be used in the human body for medical applications. (Half-life is the amount of time it takes for 50 per cent of the radioactive particles to decay by emitting some combination of alpha, beta and gamma radiation). For the purposes of medical treatment, a shorter half-life is generally better. CNL works with the isotope Actinium 225 which has a half-life of 10 days. This is long enough for researchers to incorporate it into a radiopharmaceutical which has time to circulate in the body, collect in target areas and emit high energy alpha particles to cells immediately surrounding it, but short enough that it decays to stable products without adverse dose consequences.